1. Field of the Invention
This invention is directed to clamping devices and drawbars for screens mounted on vibratory screening system; to such items for tensioning screens in vibratory separators; to systems with such devices; to screens for such systems and to methods of their use.
2. Description of Related Art
There are a variety of known devices and apparatuses for securing a screen to a vibratory screening apparatus. Many of these systems employ a simple bolt, nut, and plate combination, with or without springs or shock absorbing material. Tightening and loosening of the nut provides tension adjustment. In many of the these systems, multiple screen tensioners on each end of a screen are used for each individual screen. In some cases multiple screen tensioners are required along a screen side because a tension rail may bow providing unequal tension along the screen side. The use of multiple tensioners on each screen side or end requires a relatively long time to change screens since each individual screen tensioner must be released and then tightened. Prior patents include, but are not limited to, U.S. Pat. Nos. 4,303,509; 5,332,101; 5,392,925; and 6,179,128 all of which (and all the references cited in them) are incorporated fully herein for all purposes.
Typically a screen tensioning clamp, plate, bar or member (sometimes referred to as xe2x80x9ctension rails,xe2x80x9d drawbars,xe2x80x9d xe2x80x9cbrackets,xe2x80x9d or xe2x80x9cside railsxe2x80x9d) has a squared-off upper edge that can wear against a shaker""s basket wall or other side wall or member. One attempted prior solution to this problem was to weld a plate to a basket side wall and to position the tensioning member""s upper edge so that it contacts and wears against this plate (see U.S. Pat. No. 5,332,101).
xe2x80x9cHookstripsxe2x80x9d are used, as is well-known on screen ends to provide a surface or channel against which part of screen tensioner bears to tighten a screen in place on a separator or shaker apparatus. Typically such hookstrips have a squared-off outer portion that bears against and wears against a basket wall or other side wall or member. Also, a tensioning member often has a squared-off lower edge that bears against and wears against part of a hookstrip. Reduction of the wearing of these parts is desirable.
The prior art teaches that it is ideal to apply uniform screen tension in and across screen assemblies installed in vibratory separators such as, but not limited to, shale shakers. When multiple screen tensioners are used at each end of a screen, efforts have been madexe2x80x94which often are unsuccessfulxe2x80x94to insure that each screen tensioner applies the same amount of tension to a screen. If part of a screen is not tensioned properly, it may not perform properly and may lead to screen damage.
U.S. Pat. No. 5,332,101 discloses a screen tensioning structure that includes body members with a cam arrangement whose movement creates a pulling effect when cam followers slide up camtracks. As shown in the patent, a plurality of screen tensioning devices are used for each individual screen with multiple screen tensioners on each end of the screen. Certain commercially available embodiments require a special wrench to turn a movable adjustment nut.
There have long been needs, recognized by the present inventors, for: an efficient screen tensioning clamp apparatus only one of which is needed on each screen end to effectively mount a screen to a vibratory separator or shale shaker; for such an apparatus that can be used with existing vibratory system screen mounts without requiring changes and alterations to the vibratory system or to the screens to be mounted thereon; for such an apparatus which is easily installed, and relatively quickly installed so that installation personnel have minimal exposure to vapors and materials associated with the use of vibratory separators; for such an apparatus that reduces misalignment between the apparatus and structural members of the vibratory system; for such an apparatus and separators with it which applies uniform tension across a screen; for tensioning apparatus with which wear on it and on parts of baskets or other side walls is reduced; for such apparatus with which friction between drawbars and basket walls is reduced; and for such an apparatus that counters the tendency of screen ends to bow out from a basket wall when screen tensioners are tightened.
The present invention, in certain embodiments, provides a screen tension clamping apparatus that has one elongated draw bar that co-acts with a screen end hookstrip and is tensioned with a single bolt structure. In certain aspects, the single drawbar is substantially equal in length to the length of the screen end (or side) with which it is in contact. In one particular aspect the drawbar has an edge that is crescent shaped or curved to accommodate the typical slackening or bowing of the outer sides at the end of a screen that is put under tension on a vibratory separator or shaker. This curved shape insures that the ends of the screen are tightened as is the rest of the screen. Alternatively, the single drawbar has sufficient strength, e.g. by making it sufficiently large and/or massive, that tightening the drawbar prevents less tension being applied to the screen end""s outer parts which can result in undesired inward bowing of a screen.
In another aspect the present invention provides a screen that has ends that are curved to compensate for the bowing of certain prior art tightened screen ends. In certain embodiments such a screen has similarly curved hookstrips to offset the curving or bowing of screen ends. In one aspect such a screen is mounted on a frame that has similarly curved ends to accommodate curved screen ends. Such a screen may or may not, according to the present invention, be mounted with the drawbars according to the present invention (drawbars with straight surfaces or, as described below, with a curved or crescent-shaped surface).
The present invention, in certain aspects, provides a vibratory screen apparatus which includes; a basket for mounting of one or more screens; one or more screens releasably mounted to the basket with any tension clamping devices described above or herein; and one or more vibratory devices for vibrating the basket and/or screen. The screens may be any screen described or disclosed herein. The screens may be mounted with any tensioner according to the present invention disclosed herein.
Using a spring of sufficient spring force that not all of the spring force is applied can facilitate correct tensioning and uniform tensioning of systems according to the present invention, i.e. such systems may be more xe2x80x9cfool-proofxe2x80x9d than past systems in that a substantially equal amount of tension is applied by each rail or drawbar. More uniform screen tension produces more uniform material separation results.
What follows are some of, but not all, the objects of this invention. In addition to the specific objects stated below for at least certain preferred embodiments of the invention, other objects and purposes will be readily apparent to one of skill in this art who has the benefit of this invention""s teachings and disclosures. It is, therefore, an object of at least certain preferred embodiments of the present invention to provide new, useful, unique, efficient, nonobvious screen tension clamping apparatuses, vibratory screen systems with such apparatuses, plates for such apparatuses, and methods of their use.
Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures and functions. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims to this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that the conceptions of this disclosure may be used as a creative basis for designing other structures, methods and systems for carrying out and practicing the present invention. The claims of this invention are to be read to include any legally equivalent devices or methods which do not depart from the spirit and scope of the present invention.
The present invention recognizes and addresses the previously-mentioned problems and long-felt needs and provides a solution to those problems and a satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one skilled in this art who has the benefits of this invention""s realizations, teachings, disclosures, and suggestions, other purposes and advantages will be appreciated from the following description of preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this patent""s object to claim this invention no matter how others may later disguise it by variations in form or additions of further improvements.